(a) What was the basis of Mendeleev’s classification of elements?
(b) List two achievements of Mendeleev’s Periodic table.
(c) List any two observations which posed a challenge to Mendeleev’s periodic law.
Mendeleev classified elements according to their atomic masses .
- Mendeleev was able to classify all the 63 elements that had been discovered at that time.
- He left gaps for the elements yet to be discovered and also predicted their properties.
- Since Mendeleev arranged the elements according to their atomic masses, the position of isotopes (which have the same mass number but different atomic number) could not be decided.
- The position of Hydrogen could not be decided.
- Since the atomic mass increases irregularly from one element to the next, this makes it difficult to predict the position of undiscovered elements.